U.S. patent application number 12/439283 was filed with the patent office on 2010-01-28 for rotor for a permanent-magnet electrical machine.
This patent application is currently assigned to ABB OY. Invention is credited to Jere Kolehmainen.
Application Number | 20100019597 12/439283 |
Document ID | / |
Family ID | 36950683 |
Filed Date | 2010-01-28 |
United States Patent
Application |
20100019597 |
Kind Code |
A1 |
Kolehmainen; Jere |
January 28, 2010 |
ROTOR FOR A PERMANENT-MAGNET ELECTRICAL MACHINE
Abstract
The object of the invention is a rotor for an electrical machine
excited by permanent magnets, said rotor comprising a substantially
cylindrical magnetic body of the rotor fitted onto the shaft of the
electrical machine and a set of permanent magnets used to create a
first and a second pole alternately in the circumferential
direction, excited in opposite directions. The permanent magnets
are fitted into openings arranged within the rotor. The rotor
comprises a body part with several segments extending to the outer
circumference in the circumferential direction and an outward
tapered section remaining between the segments in the radial
direction of the rotor. Permanent-magnet pieces are arranged
between each section and segment.
Inventors: |
Kolehmainen; Jere;
(Merikaarto, FI) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
ABB OY
Helsinki
FI
|
Family ID: |
36950683 |
Appl. No.: |
12/439283 |
Filed: |
August 31, 2007 |
PCT Filed: |
August 31, 2007 |
PCT NO: |
PCT/FI07/00218 |
371 Date: |
March 6, 2009 |
Current U.S.
Class: |
310/156.11 ;
310/156.56 |
Current CPC
Class: |
H02K 1/2766
20130101 |
Class at
Publication: |
310/156.11 ;
310/156.56 |
International
Class: |
H02K 1/27 20060101
H02K001/27; H02K 21/12 20060101 H02K021/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2006 |
FI |
20060785 |
Claims
1. A rotor for an electrical machine excited by permanent magnets,
comprising a substantially cylindrical magnetic body of the rotor
fitted onto the shaft of the electrical machine and a set of
permanent magnets used to create a first pole and a second pole
alternately in the circumferential direction, excited in opposite
directions and fitted in openings arranged within the rotor, a
permanent magnet being fitted at least on the edge of each pole,
wherein the rotor comprises a body part with several segments
extending to the outer circumference in the circumferential
direction, said segments having an outer side forming the outer
circumference of the rotor and edges on both sides constituting a
substantially equal acute angle with the outer side, creating a
section tapered smoothly outwards in the radial direction of the
rotor between adjacent segments, and wherein permanent-magnet
pieces are arranged between each section and segment.
2. A rotor according to claim 1, wherein the segments and the
outward tapered sections and the permanent-magnet pieces constitute
a shape-locked structure with regard to centrifugal forces.
3. A rotor according to claim 1, wherein the segments form the
first pole and the tapered sections form the second pole.
4. A rotor according to claim 1, wherein the permanent magnets on
the edges of the pole excited in the second direction are slanted
in relation to each other in the radial direction of the rotor and
that wherein the permanent magnets are closer to each other at the
end facing the outer circumference of the rotor compared to the end
facing the shaft of the electrical machine, making the pole tapered
outwards.
5. A rotor according to claim 4, wherein the outward tapered pole
has a third permanent magnet located between the ends of the
permanent magnets on the edge facing the shaft.
6. A rotor according to claim 1, wherein the pole excited in the
first direction is formed of a first section (126), and the pole
excited in the second direction is formed of the next section in
the circumferential direction of the rotor.
7. A rotor according to claim 6, wherein the sections are
substantially wider than the segments remaining between them.
8. A rotor according to claim 6, wherein there is a third permanent
magnet between the ends of the permanent magnets on the edges of
the poles facing the shaft of the rotor.
9. A rotor according to claim 1, wherein the rotor parts forming
the first and the second pole are separate from each other.
10. A rotor according to claim 9, wherein an extrusion is formed at
the edge of the segment on the outer edge of the rotor, overlapping
the end of the permanent magnet.
11. A rotor according to claim 9, wherein an extrusion is formed at
the edge of the section on the outer edge of the rotor, overlapping
the end of the permanent magnet.
12. A rotor according to claim 1, wherein the adjacent segments and
sections are connected to each other by a narrow neck of
material.
13. A rotor according to claim 1, wherein the rotor body, segments
and/or sections are manufactured of ferromagnetic sheets.
14. A rotor according to claim 1, wherein the rotor body, segments
and/or sections are cast.
15. A rotor according to claim 1 wherein the rotor body, segments
and/or sections are manufactured of magnetically conductive powder
metal.
16. A rotor according to claim 2, wherein the segments form the
first pole and the tapered sections form the second pole.
17. A rotor according to claim 2, wherein the pole excited in the
first direction is formed of a first section, and the pole excited
in the second direction is formed of the next section in the
circumferential direction of the rotor.
18. A rotor according to claim 7, wherein there is a third
permanent magnet between the ends of the permanent magnets on the
edges of the poles facing the shaft of the rotor.
19. A rotor according to claim 2, wherein the rotor parts forming
the first and the second pole are separate from each other.
20. A rotor according to claim 3, wherein the rotor parts forming
the first and the second pole are separate from each other.
Description
[0001] The object of the invention is a rotor for a
permanent-magnet electrical machine according to the preamble of
claim 1.
[0002] Electrical machines excited by permanent magnets have been a
competitive alternative for several years. In particular,
synchronous machines excited by permanent magnets have become more
common in various applications owing to their simple structure and
ease of control. Permanent magnets fitted onto the rotor are used
to create the field that excites the electrical machine, and two
structural solutions are available. Either the permanent-magnet
pieces are installed onto the outer surface of the rotor, or the
permanent-magnet pieces are installed into the rotor. The present
invention concerns the latter structural alternative--that is, a
synchronous machine excited by permanent magnets in which the
permanent-magnet pieces are embedded into the rotor. More
precisely, in the object of the invention, the permanent-magnet
pieces are located within the rotor's frame or pole pieces
assembled of magnetically conductive parts so that when viewed in
the axial direction of the machine, the permanent-magnet pieces are
nearly radial to the rotor at least in part, and the main magnetic
flux originating from the pieces bends in the rotor between two
permanent magnets through the magnetically conductive parts towards
the air gap of the machine, constituting the rotor's magnetic
pole.
[0003] In rotors implemented with permanent magnets, the magnetic
flux generated with permanent magnets must be guided to go as
perfectly as possible over the air gap to the stator of the
electrical machine and further through the stator's magnetic body
back over the air gap to the rotor. Any stray flux that does not
follow the intended and designed route will deteriorate the
electrical machine's operating characteristics and efficiency. One
of the factors deteriorating the magnetic characteristics of the
rotor is caused by magnetically conductive parts at the end of the
permanent magnets facing the air gaps that constitute a route for
the flux from one pole to another. One of the reasons for this
structural solution is the mechanical durability required of the
rotor, particularly against centrifugal forces.
[0004] For example, a synchronous-machine rotor is known from the
application publication US2003/0173853 A1 in which the permanent
magnets are fitted between two segments formed of metal sheet. In
this solution, an extrusion or cam is formed in the segments, and
the edge of the permanent magnets facing the outer circumference
rests on the extrusion or cam due to the effect of centrifugal
forces.
[0005] The purpose of the present invention is to develop a new
structural solution for a permanent-magnet rotor in which the
centrifugal forces affecting the different parts of the rotor are
in control, the magnetic flux follows the planned route and any
stray flux from one pole to another is minimised. In order to
achieve this, the invention is characterised by the features
specified in the characteristics section of claim 1. Certain other
preferred embodiments of the invention are characterised by the
features listed in the dependent claims.
[0006] The solution according to the invention makes the structure
of a permanent-magnet rotor rigid, and all of the structural parts
of the rotor are supported by the rotor body part that is directly
attached onto the rotor shaft. The rotor body is shaped so that it
contains several segments extending to the outer circumference of
the rotor, with both sides of the segments forming an acute angle
with the surface of the part in question adjacent to the outer
circumference of the rotor. Therefore a part or section with a
triangular or nearly trapezoidal cross-section is formed between
adjacent rotor body parts extending to the outer circumference,
said part or section being narrower at the outer circumference of
the rotor compared to the other end of the area that is closer to
the shaft. The part fitted into this section is supported by the
sides of the body part segments and is locked in place in the
radial and tangential directions. This creates a shape-locked
structure, the parts of which will stay in position also at high
speeds and over great variations in speed without any separate
support elements. The solutions according to the invention supports
the pole structure against the forces towards the axis of the rotor
and towards outer surface of the rotor.
[0007] The side edges of the sections and the side edges of the
segments on the opposite sides of the permanent magnets are
straight and the sections are smoothly tapering towards the outer
circumferential surface of the rotor. The structure is simple and
the permanent magnets can be made of one piece in the radial
direction.
[0008] According to a preferred embodiment of the invention, the
segments connecting to the rotor body part are substantially
narrower than the outward tapered sections remaining between them.
According to the embodiment, the permanent magnets arranged between
the sections and segments are excited so that only the sections
form the poles of the rotor, while the segments implement the
support function according to the invention. This solution provides
a machine with a smaller number of poles and a higher rotational
speed.
[0009] According to a preferred embodiment, the magnetically
conductive parts of the rotor are manufactured of sheets assembled
into a sheet pack. In this case, the parts constituting the segment
and the section can be connected to each other with narrow necks of
material. Alternatively, the necks can be removed fully or
partially after assembly of the rotor is completed. Of the sheets,
the segments and sections can be manufactured separately, in which
case the segments, and correspondingly the sections, are made
uniform by bolting or gluing, for example.
[0010] According to yet another embodiment, the rotor body part and
the segments and sections related to it are manufactured by
casting. In this case, the parts are appropriately machined after
casting. Alternatively, they can be manufactured of powder metal.
The different parts can also be manufactured in different ways,
e.g. the body part and the segments of a sheet pack and the
sections of powder metal, etc.
[0011] According to an embodiment, the sections and segments are
separate from each other and can be manufactured separately.
[0012] In the following the invention will be described in more
detail with the help of certain embodiments by referring to the
enclosed drawings, where
[0013] FIG. 1 illustrates the cross-section of a rotor according to
the invention,
[0014] FIG. 2 illustrates the cross-section of another rotor
according to the invention,
[0015] FIG. 3 illustrates a solution according to the invention in
which the cavity of a permanent magnet is open to the air gap,
[0016] FIG. 4 illustrates another solution according to the
invention in which the cavity of a permanent magnet is open to the
air gap,
[0017] FIG. 5 illustrates different alternatives for implementing
the permanent-magnet pieces and
[0018] FIG. 6 illustrates an alternative solution according to the
invention in which the cavity of a permanent magnet is open to the
air gap.
[0019] FIG. 1 illustrates a solution implemented according to the
invention as a cross-section viewed in the direction of the rotor
shaft 2. The rotor 4 is created using a well-known method by
stacking ferromagnetic sheets 6 into a sheet pack, and a shaft 2 is
installed in the middle into holes die-cut into the sheets for the
purpose. The holes, like the openings in the sheet for the
permanent-magnet pieces, can also be formed using the well-known
methods of laser cutting or water cutting. The outer circumference
of the rotor is slightly waved or heart-shaped so that at the
middle of the magnetic poles, the radius of the rotor is greater
than between the poles. The shape of the rotor's outer
circumference is not crucial for the present invention; it can also
be round or piecewise curved as illustrated by the examples in
FIGS. 3 to 5. The sheets 6 also have die-cut elongated openings 12
and 14 that, in their longitudinal direction, extend from the
inside part of the rotor close to the outer circumference and that
are slightly slanted in relation to the radius of the rotor. The
openings 12 and 14 are located alternately in the circumferential
direction of the rotor and are formed so that the openings 12 are
slanted from the radial direction to the right and the openings 14
are slanted from the radial direction to the left. At the end
facing the circumference of the rotor, the distance between the
openings 12 and 14 is substantially equal around the entire rotor.
Permanent-magnet pieces 18 are installed in the openings 12 and
permanent-magnet pieces 20 are installed in the openings 14 so that
the direction of excitation of the permanent-magnet pieces 18 is
clockwise and the direction of excitation of the permanent-magnet
pieces 20 is counter-clockwise as illustrated with the arrows
.PHI.. Thus, on the outer circumference of the rotor in the
circumferential direction, there are alternately N poles formed of
the sections 26 and S poles formed of the segments 24. It is
obvious to a person skilled in the art that the S poles and N poles
can also be the other way round. At the inner ends of the openings
12 and 14, there are tangential elongated openings 16 that, when
going clockwise, are between the end of the opening 12 and the end
of the opening 14. Permanent magnets 22 are fitted into the
openings 16 so that they excite in the same direction as the
adjacent permanent magnets 18 and 20. Thus, in the case illustrated
in FIG. 1, the openings 16 and the permanent magnets 22 are at the
N poles.
[0020] According to FIG. 1, the shape of the sections 26 forming
the N poles is tapered outwards, and the shape of the segments 24
forming the S poles is broadening outwards.
[0021] The parts of the sheet pack forming the poles 24 and 26 in
the rotor are integral to the inner part of the rotor 28 that is
attached onto the shaft 2. The S poles 24 are connected to the
inner part of the rotor body 28 with a wide area 30, so the S poles
24 constitute a strong and solid uniform piece with the inner part
of the rotor. The sheets of the N poles 26 are connected to the
sheets of the S poles on the outer circumference of the rotor with
narrow necks or connecting strips 32 on both edges. Furthermore,
the sheets of the N poles 26 are connected between the ends of the
openings 12 and 16 and, correspondingly, openings 14 and 16 facing
each other with another set of necks or connecting strips 34. The
width of the necks 32 in the circumferential direction of the rotor
is as small as possible to minimise the stray flux going through
them. Correspondingly, the width of the neck 34 is small in order
to prevent stray flux through it from an N pole to the adjacent S
pole. The necks 32 and 34 must retain the integrity of the sheets
during sheet pack manufacture and bear the forces imposed on them
during operation.
[0022] According to the inventive idea of the patent, radial forces
imposed on the N pole 26, such as centrifugal forces, push the N
pole outwards, making its side parts contact the permanent-magnet
pieces 18 and 22 on its edges that will further contact the slanted
side parts of the S poles 24. When the S poles are tightly
connected to the shaft 2 through the inner part 28 of the rotor,
the N poles 24 and the permanent-magnet pieces 18 and 22 between
the S and N poles are also reliably supported on the rotor body and
shaft. Correspondingly, the permanent-magnet pieces 22 between the
N poles and the inner part of the rotor are similarly supported
against radial forces through the N poles 26.
[0023] FIG. 2 illustrates another permanent-magnet rotor according
to the invention for an electrical machine in which the number of
poles is six. The rotor 104 deviates from the embodiment
illustrated in FIG. 1 so that the rotor poles are constructed
differently and that the direction of excitation of the
permanent-magnet pieces is different, as described in more detail
below. The rotor 104 is created by stacking ferromagnetic sheets
106 into a sheet pack, and a shaft 2 is installed in the middle
into holes die-cut into the sheets for the purpose. The sheets 106
also have die-cut elongated openings 112 and 114 that, in their
longitudinal direction, extend from the inside part of the rotor
close to the outer circumference and that are slightly slanted in
relation to the radius of the rotor. The openings 112 and 114 are
located alternately in the circumferential direction of the rotor
and are formed so that the openings 112 are slanted from the
rotor's radial direction to the right and the openings 114 are
slanted from the radial direction to the left. Permanent-magnet
pieces 118 and 119 are alternately installed in the openings 112 so
that the direction of excitation of the permanent-magnet piece 118
is clockwise and the direction of excitation of the
permanent-magnet piece 119 is counter-clockwise as illustrated with
the arrows .PHI.. Permanent-magnet pieces 120 and 121 are
alternately installed in the openings 114 so that the direction of
excitation of the permanent-magnet pieces 120 is counter-clockwise
and the direction of excitation of the permanent-magnet pieces 121
is clockwise. Thus, in the outer circumferential direction of the
rotor, there are alternately S poles formed of the sections 124 and
N poles formed of the sections 126. Segments 125 and 127 remain
between the sections 124 and 126. At the inner ends of the openings
112 and 114, there are tangential elongated openings 116 that, when
going clockwise, are between the end of the opening 112 and the end
of the opening 114. Permanent magnets 122 and 123 are fitted
alternately into adjacent openings 116 so that the permanent
magnets 122 are at the S poles 124 and excite towards the rotor
shaft 2, and the permanent magnets 123 are at the N poles 126 and
excite the rotor's circumference 140. In the embodiment according
to FIG. 2, the outer circumference of the rotor is gently waved
similarly to the case in FIG. 1 so that at the poles 124 and 126,
the radius of the rotor is slightly greater than between the
poles.
[0024] In the embodiment illustrated in FIG. 2, the shape of both
the N poles 126 and the S poles 124 is tapered outwards. The shape
of the segments 125 and 127 remaining between the poles 124 and 126
is broadening outwards. The parts of the sheet pack forming the
poles 124 and 126 in the rotor, as well as the segments 125 and
127, are integral to the inner part of the rotor 28 that is
attached onto the shaft 2. The segments 125 and 127 are connected
to the inner part of the rotor body 28 with wide areas 130, so the
segments 125 and 127 constitute a strong and solid uniform piece
with the inner part of the rotor. The sheets of the sections 124
and 126 forming the poles are connected to the sheets of the
segments on the outer circumference of the rotor with narrow necks
or connecting strips 132 on both edges. Furthermore, the sheets of
the pole sections 124 and 126 are connected between the ends of the
openings 112 and 116 and, correspondingly, openings 114 and 166
facing each other with another set of necks or connecting strips
134. The width of the necks 132 in the circumferential direction of
the rotor is as small as possible to minimise the stray flux going
through them. Correspondingly, the width of the neck 134 is small
in order to prevent stray flux through it from an N pole to the
adjacent S pole. The necks 132 and 134 must retain the integrity of
the sheets during sheet pack manufacture and bear the forces
imposed on them during operation.
[0025] The width of the areas 130 is substantially greater than the
width of the necks 132 and 134 in order to create a sufficient
supporting piece. Correspondingly to the embodiment in FIG. 1,
according to the inventive idea, all parts of the rotor are
supported against radial forces. Centrifugal forces imposed on the
sections 124 and 126 push the pole parts outwards, making their
side parts contact the permanent-magnet pieces 118 and 119 and,
correspondingly, 120 and 121 on the edges that will further contact
the slanted side parts of the segments 125 and 127. When the
segments are tightly connected to the shaft 2 through the inner
part 28 of the rotor, the sections 124 and 126 and the
permanent-magnet pieces 118-121 on their sides are also reliably
supported on the rotor body and shaft. Correspondingly, the
permanent-magnet pieces 122 and 123 between the poles and the inner
part of the rotor are similarly supported against radial forces
through the sections 124 and 126 constituting the pole parts.
[0026] In the embodiments illustrated in FIGS. 1 and 2, the
adjacent pole parts of the rotor and, correspondingly, the pole
parts and the segments between the poles, are connected to each
other with narrow necks of material at the ends of the magnet
openings. The following is a description of alternative embodiments
in which the necks connecting the pole parts to the rotor are
missing completely or from some magnet openings. FIG. 3 illustrates
the cross-section of one pole 224 of the rotor in the axial
direction of the rotor, in which the magnet openings 312 and 314
are open near the circumference of the rotor. There is a fixing lug
or extrusion 316 formed on the outer edges of the pole section 224,
overlapping the end of the permanent-magnet piece 318. At the other
end, the magnet openings are closed as in the examples of FIGS. 1
and 2. In the embodiment of FIG. 3, the stray flux route is blocked
on the outer circumference through the magnetic sheet between the
section 224 and the adjacent segment 226, which reduces stray flux
close to the air gap of the machine. However, the segments and
sections of the rotor are integral and joined to the rotor body,
which facilitates manufacture and handling of the sheets during
sheet pack assembly.
[0027] The embodiment in FIG. 4 is otherwise similar to the
solution in FIG. 3 but in this case, the fixing lugs 416 are
arranged in the segment 426, which means that the side wall 428 of
the outward tapered section 424 is straight and ends at the end of
the permanent magnet piece 418, subsequently curving into the outer
circumferential surface of the pole 424. In the embodiments of
FIGS. 3 and 4, the outward tapered sections are also supported
against radial forces on the outward broadening segments through
the permanent magnet pieces in between.
[0028] FIG. 5 illustrates an embodiment in which there are no necks
of material between adjacent permanent-magnet openings within the
rotor and there are no necks of magnetically conductive material
between the sections and the segments, but there is a magnetically
non-conductive part 500 between the permanent-magnet pieces 516 and
522 and, correspondingly, 518 and 522 that is filled with resin,
for example. The fixing lugs 531 are arranged on the outer edges of
the segment 526 and the fixing lugs 532 are arranged on the outer
edges of the pole section 524.
[0029] The FIG. 5 suggestively illustrates a number of possible
structural solutions for permanent magnets that can also be used to
implement a solution according to the invention. The
permanent-magnet pieces 516 and 522 are curved. However, the
permanent-magnet piece to the right of the illustrated pole 524 is
formed of two partial pieces 518 and 518' that are in a slightly
shifted position in relation to each other in the tangential
direction. In this case, the outward tapered section is completely
surrounded by magnet openings with the exception of narrow necks
close to the outer circumference of the rotor. As has been
described above, also in this case the radial forces are supported
on the rotor body through the outward broadening segment. The
embodiments of permanent-magnet pieces illustrated in FIG. 5 are
examples, and naturally, only one embodiment is used in any single
machine. In all cases, each permanent magnet exciting a pole
consists of one or more pieces in the longitudinal direction of the
machine as is known of the art.
[0030] FIG. 6 illustrates an embodiment in which there are no necks
of material between adjacent permanent-magnet openings within the
rotor and the section 624 is separate from the segments 626 that
are on the both sides of the section 624. The fixing lugs or
extrusions 632 are arranged on the outer edges of the section 624.
On the side of the segment 626 there is a lug 633 opposite to the
lug 632. The permanent magnet 618 is locating in the opening that
is formed of the lugs 632 and 633 at the ends of the permanent
magnet 618 and of the side edge 634 of the section 624 and of the
side edge 635 of segment 626. The section 624 is supported against
the centrifugal force via the permanent magnet 618 and the side
edge 635 of the segment. Further the section is supported against
the force towards the centre of the rotor via the permanent magnet
618 and the lug 633. The opening 636 between the section and the
inner part of the rotor body 628 is empty. Naturally, a piece of
permanent magnet can be positioned into the opening, if additional
magnetizing flux is required. Alternatively the opening can be
filled with some other material for supporting or fixing
purposes.
[0031] Further to the permanent-magnet openings being half-open
towards the outer circumference of the rotor--that is, the air gap
of the machine--as described above, they can also be fully open
within the scope of the inventive idea.
[0032] The invention has been described above with the help of
certain embodiments. The embodiments of the invention may vary
within the scope of the following claims.
* * * * *